ci(deps): update matplotlib requirement from <4,>=3.8 to >=3.11.1,<4 (#62)

Updates the requirements on [matplotlib](https://github.com/matplotlib/matplotlib) to permit the latest version.
- [Release notes](https://github.com/matplotlib/matplotlib/releases)
- [Commits](matplotlib/matplotlib@v3.8.0...v3.11.1)

---
updated-dependencies:
- dependency-name: matplotlib
  dependency-version: 3.11.1
  dependency-type: direct:production
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements.txt

@@ -10,6 +10,6 @@
 # for upstream API changes and are not strict pins.
 numpy>=1.26,<3
 pandas>=2.0,<3
-matplotlib>=3.8,<4
+matplotlib>=3.11.1,<4
 statsmodels>=0.14,<1
 linearmodels>=4.27,<6